For transmitting small amounts of data, for example of data or payload data of a sensor, e.g. of a heating, electricity or water sensor, a radio transmission system may be employed. To this end, the sensor typically has a measuring means including a radio transmitter (data transmitter) attached to it which transmits the data to a data receiver by means of a burst-type data packet. In digital radio transmission systems, or radio communication systems, training sequences, or pilots, are typically used for synchronizing the data packet in the data receiver. Training sequences are deterministic or pseudorandom binary data sequences, e.g. PRBS (pseudorandom bit stream) sequences transmitted to the data receiver by the data transmitter along with the actual payload data within the data packet. The training sequences are known to the data receiver. By correlating a receive data stream with the known training sequences, the data receiver may determine the temporal position of the known training sequences in the receive data stream. In this context, the correlation function comprises, at the location of the training sequence in the receive data stream, a correlation peak which is the higher, or the larger, the better the receive data stream matches the known training sequences. The more the receive data stream, or a transmission signal, is superimposed by noise, however, the lower or smaller the correlation peak of the correlation function will be.
In the publication “A Concept for Data-Aided Carrier Frequency Estimation at Low Signal-to-Noise Ratios” by Susanne Godtmann, Niels Hadaschik, Wolfgang Steinert and Gerd Ascheid, the training sequence is subdivided into two parts spaced apart from each other, which enables performing improved frequency estimation.
In a radio transmission system wherein a code gain or coding gain is accomplished by means of code combining, i.e., by combining two or more data packets, by transmitting redundant information in several different data packets at different times, it is useful to detect the individual data packets even when the signal-to-noise ratio (SNR) is very low and is not sufficient for (fully) decoding an individual data packet. Depending on the code gain by means of said combination of several data packets, the signal-to-noise ratio that may be used for decoding and at which the data can still be detected decreases at the data receiver. However, for realizing the code gain it is useful that the individual data packets can be found or determined or partly be decoded, even incorrectly, even in the case of a low signal-to-noise ratio, in the receive data stream.